The present invention relates to a method of depositing a thin film on a polymer substrate by plasma Chemical Vapor Deposition.
Recently, environmental-conscious automobiles having a high performance is increasingly desired and most of the automobile components have been converted into those made from plastics, resulting in automobiles of lighter body weights which enable more efficient gas mileage. Especially, thermoplastic materials are considered to be attractive materials which can be recycled easily and tried to be utilized increasingly in automobile components. However, plastic materials are less excellent with regard to mechanical strength, surface hardness and friction resistance when compared with metallic materials. In addition, the surface undergoes decoloration and reduction in strength due to solar ultraviolet and heat, exhibiting poor weatherability. When taking performance and quality of automobiles into account, the application of plastics to the components are limited. Unless the function is enhanced by means of some kind of surface treatment of the plastics, no advance in introducing the plastic into the automobile components is expected.
An example of the surface treatment of the plastics as mentioned above is thin film deposition by plasma CVD. When using the plasma CVD, the temperature of the substrate is heated to 400.degree. C. or higher to remove the impurities contained in SiO.sub.2 film, resulting in an excellent coating of SiO.sub.2 film. However, a plastic material having a low heat resistance could not be coated (Sunil Wickramanayaka, Yoshinori Hatanaka, Society of Electronics Communication, Technical report, Vol.93, p.91-86, 1993). Accordingly, within the same plasma device, a polymer substrate is first plasma-treated with non-polymerizable gas such as CO, H.sub.2 and O.sub.2 to enhance the ability of binding with a film, and then the plasma polymerization of an organic silane compound is conducted in an attempt to form a plasma polymerization film having an excellent durability. However, the thin film thus obtained can be bound satisfactorily to the substrate but contains a large amount of impurities such as carbon and moisture, resulting in insufficient hardness and poor friction resistance (Publication of Laid-open Japanese Patent Application, S62-132940).
On the other hand, a reaction gas is introduced into a vacuum chamber, to which a magnetic field of 875 gauss is applied while applying microwave to obtain electron cyclotron resonance effect, which allows the microwave electric field to accelerate the electrons in the plasma, resulting in a high density plasma, utilizing a developed Electron Cyclotron Resonance plasma device.